This application claims the priority of German Patent Document 100 55 505.5, filed Nov. 10, 2000, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method for reconditioning axial-construction blades for stages of turbo-machinery that have a material deficiency resulting from wear and tear, damage, and/or dimensions that are smaller than specified, especially blades for gas turbines for which the protective surface coating is worn or damaged, in which the protective coating and/or blade material is removed over at least most of the blade, and is replaced with new blade material and/or a new protective coating.
Blades for turbo-machinery are, to some extent, complex components requiring a series of manufacturing steps, and are most frequently comprised of high-grade materials, which is manifested in high component costs or a high component value. The type of blades used in the example here are single-crystal turbine blades for gas turbine rotors, made of a nickel-based alloy and equipped with ventilated enclosures. In cases of wear and tear or lower levels of damage, repairing the blades can clearly be more economical than replacing them. Frequently, such blades are equipped with special protective coatings against mechanical abrasion, against hot-gas corrosion, or against extreme temperatures. When wear and tear or damage to the protective coating occurs, attempts are made to repair them, wherein the remains of the protective coating still present must be completely removed, if possible. This is difficult because such coatings are most often ceramic, and thus are mechanically, thermally, and chemically highly resistant. Furthermore, the coating material diffuses into the blade material, creating a very deep, firm connection that is very difficult to dissolve. As a rule, when the remaining portions of the protective coating are removed, blade material will also come off.
Currently, in the removal of coatings from blades, it is customary to combine chemical treatment steps with mechanical treatment steps, wherein the action of an acid or lye causes the structure of the coating to break up, after which material is removed, for example, via mechanical radiation. As a rule it is necessary to repeat this series of steps several times. This method of removing the coating is associated with several serious disadvantages. It is environmentally problematic in terms of its chemical side, it is time-, material-, and cost-intensive, due especially to the multiple changes between different types of processing steps, and it frequently leads to an uneven removal of material over the surface of the blade, that is, it varies in spots. This can result in an undesirable change in the shape of the blade, and thus in its aerodynamics, and a reduction in the stability of the component resulting from the unnecessary removal of blade material. As a rule, these deficiencies cannot be compensated for with the newly applied coating, or can be compensated for to a limited extent.
Attempts are also made to remove the remaining sections of protective coating and surface damage from blades by milling, if desired in combination with a subsequent grinding by hand, or using hand-operated sanding devices. This also carries with it the danger, particularly with grinding, that too much of the blade material will be removed, thus adulterating the shape of the blade.
In contrast to this, the present invention provides a method for reconditioning axial-construction blades for stages of turbo-machinery that have a material deficiency caused by wear and tear, damage, and/or dimensions that are smaller than specified, which will enable the reliable removal of damaged surface areas, and damaged protective coatings, while protecting the component itself, in a time- and cost-efficient manner, while ensuring a problem-free and optimum application of a new coating with the highest degree of profile precision.
In accordance with the invention, the actual geometry of the blade is measured, the desired geometry is determined via data processing, the desired profiles are laid over the actual profiles as accurately as possible, and an adjusted desired geometry is calculated; the adjusted desired geometry is mathematically reduced by a defined removal of the coating to a net geometry that lies within the blade material, and the net geometry is produced at least in areas of the blade by removing material, and applying new material where the material was removed. Used blades frequently exhibit deviations in their profile from the desired profile, in other words the profile center no longer lies along the axis of the shaft, or the setting angle for the profile is somewhat too large or too small, for example. This results from permanent deformations in the frequently very hot working medium (gas, steam). The invention takes this circumstance into account, in that it assigns greater importance to the profile accuracy/the desired profile than the desired position. This is reflected in the shape of the adjusted desired geometry. If a blade that is to be repaired shows no deviation in the position of its profile, over the whole blade, an adjusted desired geometry is not necessary. The net geometry can then be calculated and prepared directly from the xe2x80x9cabsolutexe2x80x9d desired geometry. This is seldom the case, however. The coating removal calculated from the adjusted desired geometryxe2x80x94or the xe2x80x9cabsolutexe2x80x9d desired geometryxe2x80x94and the actual application of the new material should be equal in terms of their thickness or distribution, in order to achieve the desired profile. It is also possible to exceed the desired profile thickness slightly, in order to provide a certain xe2x80x9cwear and tear reservexe2x80x9d.